To allow mobile terminals to perform a high speed communication via cellular communication networks, the specifications of the group 3GPP (Third generation partnership project) adopt an architecture similar to that of the service HSDPA (High Speed Downlink Packet Access) to provide throughputs up to 2 Mbps (megabits per second) via an EUDCH (Enhanced Uplink Dedicated Channel) uplink channel or HSUPA (High Speed Uplink Packet Access) for future multimedia applications in UMTS (Universal Mobile Telecommunications System). In order to automatically control acknowledgement signaling between terminals and base stations, the specifications of the group 3GPP provide to add a supplementary protocol layer HARQ (Hybrid Automatic Request), at the level of the MAC (Media Access Control) sub-layer of layer 2 of the radio interface protocols.
The new protocol layer HARQ is provided to allow the base stations of the network to transmit positive acknowledgement signals ACK to the terminal if all the packets transmitted by the terminal are correctly received by base stations or a negative acknowledgement sign signal NACK if all the packets transmitted by the terminal are not correctly received by base stations. In case of a transmission fault, then the terminal has to coordinate itself with the network in order to re-transmit the packets.
Moreover, these specifications of the group of 3GPP provide that all the cells involved in a communication with the terminal send explicitly a positive acknowledgement ACK if the transmission is correct, which increases interferences at terminal level. In addition, as far as the number of NACK is about from 10% to 20% and the number of ACK represents 90%, it would be advantageous to provide a mechanism allowing base stations to get rid of emitting ACKs to the terminal when it is possible to deduce implicitly that the data were received.
In case of a synchronous communication in which a terminal and a network expect to receive data during a predetermined time TTI (Transmission Time Interval), exchanges of acknowledgement are optimized by the method described in French patent application No. 0550910 filed on the same day by the applicant and titled “procédé d'optimisation des échanges d'information d'accusé de réception dans une communication synchrone entre un terminal et un réseau (method for optimizing exchanges of information on acknowledgement in synchronous communication between a terminal and a network)”.
In case of an asynchronous communication, base stations of a network do not expect to receive data during a predetermined time, and therefore will not be able to transmit to the terminal an acknowledgement indicating that the data was not received in case of a radio linkage problem between the terminal and the network. Then the terminal continues transmitting the data needlessly while they are not correctly received by the network.